At the present time, most mass produced carpets are either of tufted or woven construction.
Tufted carpets are made by needling pile yarns into a supporting pre-woven or non-woven fabric, called the primary backing. the woven fabric can be of jute or polypropylene, and the non-woven fabric is usually of polypropylene.
After the pile tufts have been needled into the primary backing, they are bonded to the primary backing, usually by way of a bonding agent, such as latex or other suitable adhesive material. It is common practice to add a secondary backing of woven or spun-bonded man-made fabrics or of jute, which is adhered, by pressing the backing onto the latex while still tacky. This form of construction is referred to as "tufted" carpet which is usually installed upon an underpad, the tufted carpet generally having little or no inherent tread resiliancy of its own.
The installation technique most commonly utilized with such a carpet is referred to as the "tackless" or "smooth-edge" form of installation because of the absence of any visible fasteners, thus presenting a carpet having a "smooth edge" appearance without carpet tacks.
This system was originated in 1938 by the Roberts Company. In this method, strips of plywood of approximately 1/4" thickness, by 11/2" width and in four foot lengths are installed around the perimeter of the room or the area to be carpeted. The strips are available either without nails or with pre-started nails and can be either glued or nailed to the floor. The strips have two staggered rows of steel pins, projecting points uppermost and inclined laterally at an angle of 60.degree. for installation outwardly inclined towards the wall.
With this system of installation, the carpet is placed in its approximate position on the floor and is stretched by means of the use of a power stretcher or knee kicker. Stretching in this system is essential to compensate for expansion and to take out or prevent wrinkles or buckles which will otherwise develop in use, which are unsightly and also present a tripping hazard and can shorten the life of the carpet by undue wear of such wrinkled portions.
In using the tackless installation system, the carpet must possess a sufficient degree of resilience in order that it can stretch resiliently on installation. Stretch is important to provide adequate residual tension in the carpet and on the steel pins at the perimeter of the carpet to ensure that the pins retain their grip and hold the carpet adequately secured.
In order to achieve adequate anchoring of a carpet, it is necessary that the steel pins grip into the secondary backing of the carpet. Thus, the secondary backing and the bond between the primary and secondary backing must be substantial and sufficiently rigid to provide an adequate substrate for the pins to grip and to prevent the carpet from moving off the pins and coming loose from the floor. The rigidity required of tufted carpets to afford the requisite pin holding characteristics make them hard to handle especially as the latex often has a filler or hardener, commonly referred to as "clay", mixed with it to add mass and stiffness, and provide a heavy carpet with adequate dimensional stability. The provision of such dimensional stability and an effective latex bond have apparently been found to be necessary to ensure that such carpet can be properly installed using the existing conventional tackless system without subjecting the carpet to the risk of being distorted, ripped apart or in some way unacceptably damaged. For these reasons a heavy basis weight secondary backing material is used.
This type of carpet also requires the prior installation of an underpad up to the edge of the tackless strip, but, more importantly, it is hard to handle because not only is it too stiff and lacking in maneuverability, but also it is very heavy. Under colder conditions, the carpet back becomes progressively stiffer, harder and less workable. Since the carpet is commonly manufactured in widths of 12 feet and frequently in lengths of one hundred feet, there is required a considerable amount of physical labour to carry pieces of the carpet about and to lay them correctly in the proper position.
In addition, the stretching of such a rigid carpet is a highly labour-intensive, skilled and difficult affair which involves the use of a power stretcher or knee kicker. Both require expertise to operate and it is possible to damage the carpet during this stretching process by either inserting the teeth too deeply into the carpet so that they grip and rip the underpad below the carpet, or by inserting the teeth too shallowly so that they scrape the primary backing off the carpet secondary backing, and rip or damage it. When the carpet is cold, it is difficult to get correct penetration of the teeth of the knee gripper into the carpet in order to properly stretch it.
The foam backed type of carpet, as it is called, has a Primary backing and a layer of foam or urethane bonded directly to the primary backing. However, such foam-backed carpet cannot be installed by the tackless method because the foam backing is not sufficiently strong to hold the pins of the tackless strips. Simply, the foam or urethane would rip and not hold if it were stretched onto the pins of a tackless installation.
Accordingly, foam-backed carpet products have been installed by cementing them down over the entire backing surface. Carpet installed by such procedures is often difficult to remove. The adhesive holds the foam; and when attempts are made to remove it, a delamination may occur in which the foam remains on the floor and the primary backing comes up. The resulting foam and adhesive is difficult to remove.
Also, the foam is liable to disintegrate, causing considerable difficulties. Sometimes in residential areas, foam-backed carpet is installed as a "loose-lay", being only held down by the re-installation of a quarter-round trim or by use of double sided adhesive tape.
Both loose-lay and double-sided adhesive tape do not generally hold such carpet down sufficiently, especially on heavy traffic areas or areas where heavy furniture is moved.
While foam-backed carpet has the advantage that it does not require an underpad and can usually be more readily installed, its installation techniques are not considered to be totally satisfactory because of the previously mentioned problems with gluing and taping.
A third type of carpet is a woven carpet in which the backing and the yarn are woven directly together. This type of carpet is usually installed in accordance with the same tackless method as the tufted carpet construction previously mentioned and suffers from some of the same drawbacks.